The present invention relates to a test socket which interconnects electrode terminals (lead terminals) of a device to be tested and wiring terminals to be connected to a testing apparatus by means of probes which are supported by a support block, for the purpose of testing electrical performance of the device to be tested such as an IC, before the device is actually assembled into a circuit. More particularly, the invention relates to the test socket, in which a component can be mounted between the probes.
Test for testing performance of a device (an object to be tested) such as a semiconductor wafer, an IC or a module, by inputting an electric signal to the device, has been generally conducted. In case of conducting such test of electrical performance of the device, there has been employed a test socket such as an IC socket which is provided with probes for interconnecting wiring terminals on a wiring board on which ends of leads to be connected to a testing apparatus are collected and electrode terminals (lead terminals) of the device. This test socket is constructed, as shown in FIG. 10 for example, in such a manner that a support block 72 for supporting probes 71 is formed with through holes, into which the probes 71 for signals, for power supply, and for grounding are inserted, and then, the electrode terminals (the lead terminals) of the device to be tested (not shown) which is provided on one face of the socket (an upper side in the drawing) are electrically connected to the wiring terminals of the wiring board (not shown) which is provided on the other face of the socket (a lower side in the drawing), thereby to conduct the test. A device guide 74 for positioning the device to be tested is provided on an outer face of this support block 72 at a side where the device to be tested is mounted, integrally with the support block 72 or formed as a separate component to be fixed by means of screws or the like which are not shown. In FIG. 10, reference numeral 73 designates holding plates for holding the probes 71 so as not to escape, and 76 designates positioning pins for positioning the test socket with respect to the wiring board.
With recent progress of high frequency, high speed, and high performance of the device (the above described device to be tested), various performances are required to be added to the test socket which is used for testing the device to be tested. As one of examples, it is requested that the test socket is equipped with a bypass chip capacitor. Generally, the bypass chip capacitor for the probe for power supply is mounted on a wiring pattern which is the closest to the device in electric distance, on the wiring board at a lower face side of the test socket. Specifically, as seen from the device to be tested, power passes through the probes in the test socket and the pattern on the wiring board until it reaches the chip capacitor. However, due to recent progress of high frequency, high speed, and high performance of the device, inductance component that inherently exists in the probes in the test socket may sometimes become a factor for causing instable operation of the device. For this reason, it is requested that the bypass chip capacitor is arranged more close to the device to be tested. In short, this requires such an arrangement that this chip capacitor is mounted at a position directly below the device to be tested and also above the test socket.
In the test socket in the related art, the support block for supporting the probes has been formed of resin or metal. Accordingly, it has been difficult to connect the component such as the chip capacitor between the specified probes, even if so desired.
FIG. 11 shows a side view of the test socket in the related art, in which a chip capacitor is soldered to probe tubes. In the test socket in FIG. 11, a holding plate 83 at an upper side of a support block 82 is removed, and only a holding plate 83 at a lower side of the support block is shown. This support block 82 and the holding plate 83 are formed of resin. FIG. 12 is an enlarged perspective view of FIG. 11. A chip capacitor 89 is soldered (solder is denoted by S2, in the drawings) to probe tubes 81 (herein, denoted by reference numeral 81 including the probes) at their parts projected from an upper face of the support block 82. For this purpose, a relief part, which is not shown, is provided on the holding plate 83 which is disposed on the support block 82, at a position corresponding to the chip capacitor 89 so that the holding plate 83 may not interfere with the chip capacitor 89. In FIGS. 11 and 12, a pitch between the probes 81 is 1.0 mm, a size of the chip capacitor 89 is 1.0 mm×0.5 mm×0.5 mm. Therefore, it is necessary to use a soldering tool exclusive for this purpose, and high technique for soldering is also required. Further, unless the chip capacitor 89 is attached to the two probes 81 in an accurate position, forces applied to the two probes 81 are not likely to be balanced, and so, there is such anxiety that abrasion and cracks may occur in the probes 81 and electrodes of the chip capacitor 89. In short, there occurs a problem that reliability and durability of the test socket are deteriorated. Moreover, in case where the pitch between the probes 81 is reduced to 0.5 mm which is currently a mainstream, it is necessary to use a chip capacitor which is further compact having a size of 0.6 mm×0.3 mm×0.3 mm, for example, as the chip capacitor 89 to be attached, and higher technique is required for soldering, which may result in more remarkable deterioration of reliability and durability of the test socket. Further, in case of exchanging the probes 81 for maintenance, the chip capacitor 89 which has been soldered must be removed, and soldering work must be conducted again, for attaching the chip capacitor 89 after the probes 81 have been exchanged.
FIG. 13 shows a sectional view of the test socket in the related art, employing a support block formed of metal. In the test socket in FIG. 13, while it is not shown specifically the chip capacitor is soldered to the probe tubes in the same manner as in the test socket as shown in FIGS. 11 and 12, and correspondingly, a relief part for preventing interference with the chip capacitor is formed in a fixing plate at an upper side of the support block.
Use of metallic material for a support block 92 for supporting probes 91 as shown in FIG. 13 is effective for preventing noises. A metal plate formed of brass or aluminum, for example, is used for the support block 92.
In order to enhance RF performance of the test socket (high frequency in analogue form is referred to as the high frequency, while very short pulse width and short pulse interval in digital form are referred to as the high speed, both of which are hereinafter referred to as an RF), it is necessary to form the probe 91SIG for signals in a coaxial structure, and to reliably connect the probe 91GND for grounding to the ground in vicinity of the probe 91SIG for signals. For this purpose, the probe 91SIG for signals is formed in a coaxial structure in such a manner that the probe is used as a center conductor, and an inner wall of a through hole 95 in the support block 92 is used as an external conductor, with forming a space between them. An outer diameter d of the probe 91SIG and an inner diameter D of the through hole 95 are so set as to make a determined impedance. By constructing the probe 91SIG for signals in this manner, dielectric constant becomes 1, because a hollow space is formed between the center conductor and the external conductor, and therefore the coaxial structure of the determined impedance can be obtained even at a narrow pitch, even in case where an interval between the electrode terminals becomes very small due to a recent stream of downsizing and high density of the device. The probe 91GND for grounding is inserted into the through hole 95 in the support block 92 interposing a bell-shaped metal tube 97 having slots, for example, so that the probe can be reliably brought into contact with the support block 92. On the other hand, the probe 91POW for power supply is inserted into the through hole 95 in the support block 92 interposing an insulating tube 98 so as not to get in touch with the support block 92.
In the probe 1SIG for high frequency and high speed signals, the inner diameter D of the through hole 95 in the support block 92 and the outer diameter d of the probe 1SIG for signals are set so as to satisfy the following formula (1) and so as to obtain the coaxial structure having a determined impedance Z0. In the formula (1), ∈r is a dielectric constant of dielectric substance between the center conductor and the external conductor. According to the structure as shown in FIG. 13, because an air space is formed between the probe 1SIG for signals as the center conductor and the through hole 95 of the support block 92 as the external conductor, the dielectric constant ∈r becomes 1. In this manner, it is possible to cope with the narrow pitch of the probes 91.
                    [                  Formula          ⁢                                          ⁢          1                ]                                                                      Z          0                =                              60                                          ɛ                r                                              ⁢                      log            e                    ⁢                      D            d                                              (        1        )            
In case of the test socket as shown in FIG. 13, use of the support block formed of metal is convenient for enhancing shield performance, and for constructing the coaxial probe. However, because the support block is formed of metal, there is such a risk that the chip capacitor may get in touch with the support block to make a short circuit, incurring a problem that reliability is deteriorated.